Excessive use of lights or accessories such as cellular phones, radios and the like without appropriate re-charging can rapidly reduce the output of a storage battery. In the case of an automobile storage battery or the like, the battery can readily be discharged to a level where it contains insufficient output energy to crank the engine. Accordingly, attempts have been made to automatically monitor battery output voltage and disconnect the battery from the load when the measured output voltage fails below a predetermined minimum level. Apparatus for this purpose (known as intelligent battery guards) are usually designed for universal applications having varying current requirements and have especially poor performance histories. One reason for most failures is the simplistic designs of the previous devices. Another reason is the inaccurate assumption that the voltage measured at the accessory port (usually a cigarette lighter socket) is an accurate measure of the battery's discharge condition. The most accurate measure of battery condition is accomplished by measuring the specific gravity of the electrolyte. However, this is not practical in many cases and not physically possible with sealed batteries.